The present invention relates to a driving unit, an optical unit, an imaging apparatus, and an endoscope, in which a voice coil motor is used to drive a movable part for advanceable and retractable movement.
So far a voice coil motor (VCM) have been used every so often in the form of a driving force for moving a moving unit, and with a recent progress of diagnostic technology it has been desired to make optical characteristics such as focus and the angle of field variable upon endoscopic viewing. An endoscope capable of normal viewing and magnifying viewing includes a moving means for axial movement of a moving unit including an optical lens into an imaging apparatus built in an insert part. The VCM is sometimes used as such an endoscopic moving means. In that case, normal viewing is implemented when the moving unit is moved on the wide-angle end side while magnifying viewing is implemented as the moving unit is moved toward the telephoto end side. The endoscope is more frequently used in the normal viewing mode, and when the moving unit is held in abutment against the wide-end surface by the voice coil motor, there has been the need for feeding electric current constantly through the voice coil motor so as to take hold of the position of the moving unit. This has often incurred increased power consumption of the voice coil motor, resulting in a temperature rise due to heat generated from the coil. In order to decrease electric current through the coil there has been a method proposed in the art, in which biasing force is generated by making use of magnetic flux leakage from a magnetic circuit (see Japanese Patent No. 4804325).